how to use long long int and remove segmentation fault

Question

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

int main() {
    long long int a[10^9],sum=0;
    int n,i,length;
    scanf("%d",&n);

    for(i=0;i<n;i++)
    {
        if(0<=a[i]<=10^10)
        {
        scanf("%lld",&a[i]);
        }
   }

    for(i=0;i<n;i++)
    {
        sum=sum+a[i];   
    }

    printf("%lld",sum);
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */    
    return 0;
}

i dont know the reason why i am getting the segentation fault this code runs fine for this input 1000000001 1000000002 1000000003 1000000004 1000000005

10 ^ 9 == 3; 10 ^ 10 == 0. 0<=a[i]<=10^10 is legal, but it doesn't do what you think it does. It's equivalent to (0 <= a[i]) <= 10^10. (0 <= a[i]) yields either 0 or 1; that value is then compared to 10^10, which is 0. — Keith Thompson
– Keith Thompson, Commented Jun 21, 2015 at 5:10
@KeithThompson ^ has lower priority than <=, so <= 10^10 should be change to <= (10^10). — Eric
– Eric, Commented Jun 21, 2015 at 5:35
@EricWang: Good catch! So 0<=a[i]<=10^10 is equivalent to ((0 <= a[i]) <= 10) ^ 10 (I hope I got that right this time!) — Keith Thompson
– Keith Thompson, Commented Jun 21, 2015 at 5:56
regarding this line: 'if(0<=a[i]<=10^10)' I think this is actually trying to check if the contents of a[i] is within a certain range. However, a[i] has not been set and 10^10 is 0, so the chances of a long long int located on the stack, being 0 are rather slim. — user3629249
– user3629249, Commented Jun 21, 2015 at 18:05

Eric · Accepted Answer · 2015-06-21 05:21:22Z

Issues in your code:

0<=a[i]<=10^10 is not correct, should change to 0<=a[i] && a[i]<=(10^10)
^ is a bitwise xor, not power,
In your for loop, you always compare before read element of a[], so you need to read first, then compare.
use unsigned long long, don't need int at end.

Check this code:

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

#define MAX_NUM 1000000000ULL
#define MIN_NUM 0ULL

int main() {
    int n,i;
    printf("input number count: ");
    scanf("%d",&n);
    unsigned long long a[n],sum=0;

    for(i=0;i<n;i++) {
        printf("input number[%d]: ", i);
        scanf("%llu",&a[i]);
        if(a[i]<MIN_NUM || a[i]>MAX_NUM) {
            a[i] = 0;
            printf("\t(ignored, due to out of range [%llu, %llu])\n", MIN_NUM, MAX_NUM);
        }
    }

    for(i=0;i<n;i++) {
        sum+=a[i];
    }

    printf("\nsum: %llu\n",sum);
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */    
    return 0;
}

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